I copied this off the internet, looks like you cook hemp normally then add salt.
HOW TO MAKE PARTICLES PVA FRIENDLY Until now, using particles in a PVA bag was almost impossible. Take one of the greatest carp attractors of all time, hempseed for example. If you dried it out a little before you put it in your PVA funnel web you will find that some of it floats and some can still melt the bag if it’s a little too damp. Most other particles are the same, but carp legend and previous CARPology writer, Pete Regan has found a very simple, yet very attractive-to-the-carp solution.Start by putting some water into a bait tub and then add some salt. Next, place a couple of bits of funnel mesh into the solution and see if it melts. If it does, add some more salt and repeat this process until it doesn’t dissolve. Next, transfer a few handfuls of particles into the salty solution, swill it around and then just tie up your funnel web PVA bags as normal; you don’t even need to be that careful as the salty water will not melt the PVA. Better still, you will also notice that once the salty water gets onto the PVA, it will shrink, making the bag really tight. And better than that, salt is incredibly attractive to carp, so it’s actually making the PVA bag even more irresistible to the carp!These particle PVA bags can then be fired out with a catapult – a perfect alternative method to using a noisy spod, and once submerged in the water, the PVA will melt as normal.